Bleaching and color stabilization of fatty acids and related materials



BLEACHING AND COLOR sTAamz Tro or FATTY ACIDS AND- RELATED MATERIALS 7 John M. Preston, Gilman, Ill., assignor to General Mills, Inc., a corporation of Delaware NoDrawing. Application November-12.1956 I Serial No. 622,736

2 Claims. (Cl. 202-57) This invention relates to an improved method for .dis- 'tilling fatty acids.

*Fatty acids as used in this invention relate to straight chained-mono-carboxylic acids containing -6 to 22 carbon atoms. Common sources of these acids are naturally occurring fats and oils, soapstock and tall oil. Illustrative fats and oils are soybean oil, cottonseed oil, corn oil, rapeseed oil, castor oil, linseed oil, sugar cane oil, and so forth. These acids arev used extensively in the preparation of soaps, detergents, cosmetics and numerous other uses. It will be appreciated that in many of these applications the color and color stability of the products are .of primary importance. Accordingly, fatty acids having the :best color and color stability demand a premium price from these users. I

It is, therefore, an object of this invention to teach an improved process for distilling fatty acids. The principal advantages of this improved process are that the fatty acids treated in the manner hereinafter described are bleached and have good color reversion characteristics at room temperature and good color stability at elevated temperatures.

Other objects and advantages to the process will become apparent upon reading the subsequent specification.

The principal methods employed to purify fatty acids commercially are crystallization and distillation. This invention deals only with the distillation of these acids at elevated temperatures, i. e., 175 to 300 C. and at reduced pressures, i. e., 4 to 60 millimeters of mercury. It has been discovered that the objects and advantages of this invention may be accomplished by adding hypophosphorous acid and the alkali salts of hypophosphorous acid to the fatty acids prior to their distillation. Sodium and potassium hypophosphite are two illustrative salts.

The steps involved in the practice of this invention are as follows:

Step 1.-Hypophosphorous acid or one of its alkali metal salts is added to the fatty acids prior to their introduction into the stills.

Step 2.-The fatty acids are heated under reduced pressure to vaporize them and simultaneously therewith phosphine is generated when hypophosphorous acid or its alkali salts are heated at distillation temperatures.

Step 3.-The vaporized fatty acids are cooled and condensed to yield the improved acids made possible 'by this invention.

This invention may be illustrated further by reference to the following examples in which all parts are expressed as parts by weight and all percentages are ex-' pressed as percent by weight, unless specified otherwise.

EXAMPLE I 200 gram samples of technical grade lauric acid from coconut soapstock and coconut oil were distilled at 5 mm. of mercury subsequent to the addition of 0.5% Na(H PO (Nata-Because of the phosphine generated during 2,8 76,1 74 Patented Mar. -3, 1959 2 distillation itis important to carry out the distillation in a well vented .fhood.)

In each instance the percent of distillate and residue was in the order of and 4%, respectively. Table .I shows a comparison of various treated and the original acids.

Ta le ,-I

I Coconut Soapstoclr' Coconut Oil Crude .Crude'Lauric Acid. Laurie Acid Original; Treated Original Treated Distillate Distillate .Gardner Color LT .1 LT 1 LT'l LT 1 ColorStability A NDT 4 LT l NDT 3 -L'I 1' Color Stability B NDT 7 NDT 4 NDT 7 NDI 2 1 LT throughout refers to "lighter than on the Gardner scale.

NDT'throughoutrefers-tonot; darkerthan on-the Gardnerscale.

3 The "A method for measuring color stability is a measurement of the color developed by heating-s25 ml. sample of the fatty acids at 250=l=5 C for 30 minutes, cooling to room temperature, and taking a Gardner color reading.

-The B methodformeasuring-colorstability is substantally thesame as the A method except that the sample is heated for 3 hours.

EXAMPLE II 300 gram samples of crude cottonseed fatty acids were alembjically distilled at a pressure of 5 mm. Hg and a maximum pot temperature of 275 C. To each of these samples was added prior to distillation the amount of solid Na(H 'PO shown in Table II.

EXAMPLE III Crude soybean fatty acids and crude tallow fatty acids were alembically distilled as described in Example II and the results are shown in Table III.

Table III SOYBEAN FATTY ACIDS Gardner Color Color Percent of N 3(H2P02) Added Color Stability Stalgillty 0 NDT 4 NDT 9 NDT 13 2.0 NDT 3 NDT 6 NDT 12 TALLOW FATTY ACIDS 0 NDT 2 NDT 5 LT 13 2.0 NDT 1 NDT 3 NDT 11 EXAMPLE IV Hypophosphorous acid was added to 200 gram samples of crude cottonseed fatty acids and the mixtures distilled at 5 mm. Hg and at a maximum pot temperature of. 275 C. The hypophosphorous acid was added in the form of a 50% solution. In Sample A the amount of hypophosphorous acidadded was equivalent on a mole basis to the addition of 0.1% Na(H PO and in sample color tests run on the B to 1-.0%"Na (H,PO,). The results are 'shown a Table Table IV Gardner" Color 06101- Sample Color Stability Stability I I 1A1! H BY! Control.....' 8 12 16 A s 9 13 B 4 9 EXAMPLE V r- 0.2% Na(H,PO,) was added to a crude mixture of fatty acids containing approximately 3% caproic acid,

56% caprylic acid, 34% capric acid, and 7% lauric acid and the mixture distilled in a large scale commercial operation. Table Y shows the comparison between the color characteristics of acids treated in the above manner and untreated commercially distilled acids of the same composition.

Table V Gardner Color Color Color Stability Stability H A" B Treated LT 1 ND'I 6 'NDT 11 Untreated LT 1 NDT 8 NDT 13 In the large scale treatment of acids as in Example V, precautions must be taken to safely vent the phosphine generated, It has been observed, however, that only 'minute quantities of phosphine will be carried over into v the condensed fatty acids.

-As demonstrated by the preceding Examplesflt is possible to improve the quality of distilled fatty acids by the addition of from 0.01 to 2.0% by weight of hypophosphorous acid or its alkali salts. However, the preferred range is from 0.1 to 1% Therefore, many modifications and variations of the invention as hereinbefore set forth may be made with out departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

What is claimed:

1. The process of distilling fatty acids containing 6 to 22 carbon atoms which comprises adding a compound selected from the group consisting of hypophosphorous acid and the alkali salts of hypophosphorous acid to the fatty acids prior. to distillation, heating the fatty acids to 175 to 300% C. at a reduced pressure of from 4 to millimeters of mercury to simultaneously vaporize the fatty acids and generate phosphine, and cooling said vapors to condense the improved fatty acids which have been bleached and have improved color stability at elevated temperatures and good color reversion characteristics at room temperature.

2. Theprocess of claim 1 in which the phosphite compound added prior to distillation is sodium hypophosphite.

References Cited in the file of this patent UNITED STATES PATENTS 1,909,605

Belden May' 16, 1933 2,062,837 Sheely Dec. 1, 1936 2,259,968 Andersen Oct. 21, 1941 2,483,414 Henderson Oct. 4, 1949 

1. THE PROCESS OF DISTILLING FATTY ACIDS CONTAINING 6 TO 22 CARBON ATOMS WHICH COMPRISES ADDING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF HYPOPHOSPHOROUS ACID AND THE ALKALI SALTS OF HYPOPHOSPHOROUS ACID TO THE FATTY ACIDS PRIOR TO DISTILLATION, HEATING THE FATTY ACIDS TO 175 TO 300% C. AT A REDUCED PRESSURE OF FROM 4 TO 60 MILLIMETRES OF MERCURY TO SIMULTANEOUSLY VAPORIZE THE FATTY ACIDS AND GENERATE PHOSPHINE, AND COOLING SAID VAPORS TO CONDENSE THE IMPROVED FATTY ACIDS WHICH HAVE BEEN BLEACHED AND HAVE IMPROVED COLOR STABILITY AT ELEVATED TEMPERATURES AND GOOD COLOR REVERSION CHARACTERISTICS AT ROOM TEMPERATURE. 